Modern communications standards, such as Enhanced Data for GSM Evolution (EDGE), Wideband Code Division Multiple Access (WCDMA), Bluetooth-Enhanced Data Rate (BT-EDR), Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), Long-Term Evolution (LTE), and so forth, employ complex envelope modulation schemes that impose strict performance requirements on transceivers. For example, these 2G and 3G and beyond communications standards implement power control schemes at multiple implementation layers to achieve optimized quality of service (QoS).
Accurate power level control of a wireless communications device's transmissions may ensure good interoperability along with other wireless communications devices and services sharing the same transmission medium, channel, base station, and so on. If a wireless communications device transmits at a higher power level than is needed, the wireless communications device may generate excessive noise that may negatively impact surrounding wireless communications devices, causing multiple access interference (MAI), for example. However, if the wireless communications device transmits at a lower power level than is needed, the transmission may be lost due to excessive error rates and may have transmission detectability issues, in general.
Generally, a wireless communications device may be calibrated for power level during a general calibration under normal operating conditions. However, a wireless communications device may be exposed to a wide variety of operating conditions, including but not limited to variations in operating temperature, battery voltage, operating frequency, load impedance, and so forth. These operating conditions may change during use. Therefore, if power control is operated in an open loop mode (e.g., without feedback control), the calibrated power levels may be unable to meet the stringent power level accuracy requirements of the above listed communications standards as well as additional quality of service restrictions imposed by wireless phone manufacturers and/or service providers.
Furthermore, communications standards operate in duplex (3G) or simplex (2G and 2.5G) modes in a time slot fashion. At the beginning and end of each time slot, the power level may be required to vary significantly. The abrupt power level change may have spectral implications that may impact other wireless communications devices operating in close proximity to a transmitting wireless communications device. For example, stringent transient spectral requirements, such as transient switching spectrum in EDGE and transient ACLR in WCDMA, may mandate the use of a ramping profile, which the wireless communications device is required to follow in order to meet the specified switching requirements. Again, open loop power control, due mainly to the inherent inadequacy of the calibrated power levels, may not be able to meet the specified spectral requirements.